Modulated band structure and phase transitions in calcium hafnate titanate modified silver niobate ceramics for energy storage

• An ultrahigh W rec of 5.4 J/cm 3 and a relatively high η of 66% were achieved. • Wide E g and suppression of oxygen vacancy result in an improved E b . • Good thermal stability with W rec and η over a wide temperature range. Lead-free silver niobate (AgNbO 3 , AN)-based dielectric ceramics have attracted intense attention for high-power energy storage applications since 2016 due to their electric-field-assisted antiferroelectric-ferroelectric phase transition. In this work, chemical compositions of 0.2 wt.% Mn-doped (1- x )AgNbO 3 - x Ca(Hf 0.2 Ti 0.8 )O 3 (AN-CHT x , x = 0.00–0.08) were designed and their ceramic samples were prepared in flowing oxygen via solid-state route. Our results show that the CHT modification not only enhance the antiferroelectricity stability but also the breakdown field ( E b ). Further investigation reveals that the wider band gap ( E g ) and suppression of oxygen vacancy play more important role in increasing E b of AN-CHT x ceramics. Consequently, an ultrahigh recoverable energy density ( W rec ) of 5.4 J/cm 3 together with a relatively high energy conversion efficiency ( η ) of 66% is achieved under an electric field of 300 kV/cm in AN-CHT0.06 ceramics. Meanwhile, this ceramic also exhibits a good thermal stability with W rec (4.5 J/cm 3 ) and η (69%) over a wide temperature range (25–120 °C) under external electric field of 280 kV/cm. The finding in present work indicates that modulating the band structure and oxygen vacancy of AN-based ceramics may lead to the discovery of new antiferroelectric materials with pronounced energy storage properties.